Having just got the bike going again, with a lot of help from the resident keepers of the knowledge and sleuths, I now have another Quest.

To solve the case of the "will not work" thermo fan.

The story so far:
Can get the bike upto temp, but no fan kicks in. I think from memory, I once rode it long enough to illuminate the over-temp warning light on the dash.
I got hold of "Fan System Diagnostics for Two-Valve K Bikes" by Jeff Dunkle. (http://www.ibmwr.org/ktech/fan-diagnosis.shtml), and went through it step by step.
Removed seat and tank, exposing relay nest. Removed white relay.
Did the fan motor test: jumper wire from connectors 15 & A2 - fan spins nicely.
Did the Over temp warning light test - all good.
Temperature Probe Test - Nothing...no movement on the multi-meter.
Tried disconnecting connectors from temp sensor and hot-wiring - Nothing - fan should spin.
Measured voltage at connector 15 - in that big terminal block at the very front of the frame - 12 volts when ignition turned on and 15 bridged to A2.

I admit that I'm an electrical idiot, and this is really doing my head in.
I think there must be a broken wire between the big terminal block and the fan itself (about 75mm of wiring), but that does't explain why hot-wiring the temp sensor wiring is not kicking in the fan, or that the temp sensor test is a failure.

What am I missing??

The temp sensor can be a trap. There actually 2 sensors, each one works from one of the connectors on the plug to earth (the body of the sensor).
One sensor is used for the ECU to read for the mixture settings and the temp light which comes on at 111 deg C and the other sensor comes on at 103 deg C to switch the fan on through the temp relay in the Big Black Box of Mystery under the rear of the tank. On the plug on the sensor one goes to terminal 10 on the ECU and the other to terminal E on the temp relay.
Does that help, hope so.

hi giddyup

the temp sensor is a double ended sensor ......that is it has in fact two sensors inside .....the common point is the earth - case of the sensor itself .....the sensor wiring connector has 2 pins ....which is each side of the sensors (plural )

ok you got the injector side of the system working (sensor 1 )

but you say that the sensor test shows no reading ....i would be going back through the wiring ,,,and test the cabling through from the sensor to the relay input ....didnt you do that in one of the tests ( i thought you did ) ?

so that leaves the sensor connector pins on the sensor itsself ....you might have to measure each pin in reference to the body of the sensor to see if you have similar ....results ...and maybe clean up each pin a little more ?

i think i recall some talk about one side of the temp sensor becoming ....erm ...non functional ... i believe it would be wise to confirm both ends of the sensor being "proved " to be functional ....else get a borowed sensor from someone ...to test the result of the exchange

as i said before the water stub to sensor can corrode in the threads ,,,,so please make all measurements to the body of the sensor ...not the earth of the bike ...as it doesnt take much resistance change there to affect the operation over all .....

you might measure the casing of the motor to body of the sensor to confirm or dismiss any resistance problems

hope that helps

charlie99 wrote:
but you say that the sensor test shows no reading ....i would be going back through the wiring ,,,and test the cabling through from the sensor to the relay input ....didnt you do that in one of the tests ( i thought you did ) ?

I'm getting no readings at all by measuring between E & 9.

I had this problem (no thermo fan) when I 1st bought the bike 14 months ago, and I went the easy road - I replaced the relay and when that didn't work, I replaced the sensor. Admittedly, they were both used, but unlikely they'd all be shot.

So if I'm not getting any resistance at the sensor, then there must be either:
a) a shot sensor (already replaced)
b) damaged wiring.

I'm thinking b), as it had an idiot aftermarket alarm fitted. If it were damaged, where does it go? I traced the sensor wires to a small harness running along the top of the fuel injection rail and it then joins the main harness and disappears somewhere close to the relay nest.

How can I run fresh wires to test if the existing wiring is damaged? It runs from the sensor ... to where?

I'm a bit confused as to what to do next. The fan motor test works. When I join pin 15 and A2, the fan runs.
The test says that if the fan runs when 15 & A2 are joined, then test the voltage coming out of the plug supplying the fan.(Why would you test that if the fan is working when 15 & A2 are joined?)
Where is this found? I can see the fan and I can see the wires entering the body of the fan. The other end seems to run upto the heat-sink type connector block at the very front of the frame, directly above the fan.
With the 15 pin plug removed, the fan will still spin if 15 & A2 are joined. What gives there? I would have thought that the power to feed the came from that wiring block, so how does it run if it's disconnected?

If I understood the 2 replies here, is it possible that 1/2 of the sensor is suspect, because the bike runs, but the fan won't come on?
If that's the case, how is the sensor tested, independent of the wiring? Somehow earth the multimeter black lead and try to get the red onto either post successively? Remove the sensor and do it on the bench? I'm reluctant to do it because it won't be frustration free and I've already replaced the sensor (but without being tested, who knows if it works?)

You now understand why I have let it languish for so long... It really does my head in.

Thoughts?

The temp relay is actually a circuit card. I had a non-functioning fan that I diagnosed a poor solder joints on the circuit card within the temperature relay. I would venture to open the relay and use a magnifying glass to locate any suspect solder joints. They will appear to have a grainy appearance or appear to be cracked, and not a smooth appearance as would be evident in a good solder joint. If you do find one, just carefully reheat the joint to reflow the solder. It may help to apply just a touch of new solder to the joint to help with the reflow (but it's not necessary). In my case, there was a cold solder joint on one of the pins that joined the two circuit cards. Reheating the joint, reassembling the relay and testing showed the problem fixed.

This route could be easier at this point in your diagnosis than trying to locate a defective sensor.

I agree with RobMack.

It's a known problem about the soldering of the relay on the circuit board.

Do you have any ready at the water sensor temperature?
If you do, trace the conductivity of the purple/green wire from the sensor to pin E and report back to the forum.

check for diagrams here

I have no idea if the relay/circuit board is defective or not.
What I do know, is that I can't get any reading between pins E & 9. Not even continuity between either pin and either of the 2 wires at the sensor end. so a wire must be broken. Do those wires terminate at E & 9? I'm confused again...
The circuit board may well be defective too, but it doesn't matter if there's no signal to start with.
Have I got that right?

Crazy Frog, you asked: "Do you have any ready at the water sensor temperature".
Sorry mate, but I'm not quite sure what you mean...

All good fellas.
Got the inox out and coated every connector I could find. Removed the connector from the sensor and refitted it 180 degrees out from how it would be intuitively fitted.
Fired it up, got it up to temp keeping an eye on thye overheat light which I know works, and then joy of joys, it worked.
Thanks for all your help and suggestions.

Harry.

Giddyup wrote: Removed the connector from the sensor and refitted it 180 degrees out from how it would be intuitively fitted.

Hmm....that shouldn't be possible due to the shape of the connector.

(Unless it have been modded, or unnecessery much force is used.......
and a possibly damaging the connector/contacts).




If it was the sensor that was the reason to your problem, it now have been moved
to the fuel mix.
Keep an eye/ear to how the engine is running, and check the colour at the spark plugs.
It now may run to rich at operating temp.

Now that you mention it, when it came up to temperature, it was not idling very happily.
Perhaps I should put the connector back on the way it seems it should have gone.
Yes, I'll do that and see if anything changes. Thanks...

Measure the resistance to ground at both sensor elements (preferably with the
sensor connected), and compare with the diagram in the troubleshooting guide
at the portal.

Between contact # 10 and 13 at the L-jetronic multi connector.
And E and 31 at the fan relay socket.

You should measure ~same resistance at both elements.

If the motor ran nicely but the thermo fan wouldn't work when the terminal was correctly fitted, and changing the orientation of the connector results in the thermo fan working but the motor not running properly, is this conclusive proof that the sensor is faulty?

Sounds like a correct conclusion...to confirm measure as described in the
previous post.

Put a new sensor in and it all works.
And to think I came close to cutting off my own head because of this.

onya mate .....solved another one huh ?....coool

Congrats.........

So the tremp has some thing to do with how it runs right?

yep sure does

if it has a high resistance it over fuels the system....as if it were cold ...and visa versa with the fan control ,,